It is now being widely practiced to stick flexible protective films having excellent contour-following properties to, for example, the surfaces of aluminum wheels as automobile parts in order to prevent them from suffering from soil or flaw on the surfaces during the storage or transportation after manufacturing of the automobiles and to peel the protective films at the time of sale.
The sticking of a sheet to the surface of a large-sized work with an uneven surface (nonflat surface), such as the above-mentioned sticking of protective films to automobile wheels, has been carried out by the manual work of workers.
The reason for the need of the manual work is as follows. The above-mentioned protective films for automobile wheels and other flexible sheets themselves have small thicknesses and hence inherently have substantially no capability of shape retention. Thus, the attempt to adhere the sheet to the surface of a large-sized work with an uneven surface by pressing the sheet against the surface while mechanically holding two ends of the sheet encounters extreme difficulty in attaining the adherence in such a condition that the sheets follow the uneven contour of the work. Such machine operation is likely to cause various problems, include formation of an air layer between the work and the sheet, wrinkling of the sheet and inclination for coiling and peeling of the sheet at the periphery of the sheet.
In order to cope with these problems, for example, Japanese Patent Publication No, 4464/1990 proposes an automatic process for the above type of sheet, comprising providing a mold having a molding surface with an unevenness opposite to that of a surface of the work (molded item) to which the sheet is to be stuck, molding a sheet having a configuration following the contour of the molding surface of the above mold, and pressing the sheet against the surface of the work (molded item) to which the sheet is to be stuck while retaining the configuration of the sheet to thereby attain sticking of the sheet.
However, the above-mentioned conventional sheet sticking by the manual work of workers consumes enormous labor to thereby cause the productivity to be extremely poor.
On the other hand, in the process disclosed in Japanese Patent Publication No. 4464/1990, it is needed to provide, for each different work, a mold having a molding surface with an unevenness opposite to that of a surface of the work to which the sheet is to be stuck, and to employ the mold in conformity with the work. Not only does this require considerably time-consuming mold control but also the fabrication of the mold is pretty difficult. Further, the molding by the use of the mold inevitably requires mold closing and opening operations, which become a bottleneck in a sequence of sheet sticking operations to thereby cause the productivity to be poor.
Still further, in the above molding of a sheet having a configuration corresponding to the contour of the surface of the work to which the sheet is to be stuck and directly pressing of the sheet against the surface of the work to which the sheet is to be stuck while retaining the configuration of the sheet, not only would the sheet be wrinkled at the time of the sheet molding following the contour of the molding surface of the mold, e.g., when the surface of the work to which the sheet is to be stuck is uneven, air would remain between the sheet and the work to thereby form an air layer therebetween, but also the pressure at the periphery of the sheet would be so poor as to cause inclination for coiling and peeling of the sheet at the periphery.